Process for ascertaining the resistance to rusting shown by iron, steel, and iron alloys



Patented May 21, 1929. I

UNITED STATES PATENT OFFICE;

cam. mumia, or VIENNA, ausram.

raoonss roa Ascnammme 'rna nnsrsrancn r aus'rme snown men, s'rnm,

AND mom ALLOYS. 4

No Drawing. Application filed July 11, 1927, Serial No. 205,057, and in Austria July 22, 1920.

'This invention relates to a method or process for ascertaining systematically and methods in which the loss of weight by cor- 5 rosion, is made use of for determining the infiuence of oxygen upon iron or steel.

I have discovered, that to each alloy of iron and steel corresponds a certain characteristic and critical concentration and temperature of an appropriate chemical solu-- 'tion, at which the surface of the metal unites with the oxygen of the solution. I have further discovered, that this property affords a reliable means, never used heretofore, for characterizing and measuring the absolute or the relative resistance to rusting in the case of the so-called rust-proof steels. The affinity of oxygen with respect to iron, iron and steel alloys is determined systematically and gradually by my process. It indicates in a reliable manner the resistance against rusting, that is the relative or absolute rusting resistance. a

The process according to the present invention consists in that I determine that temperature (which corresponds to the characteristic critical concentration of a hot oxygenous chemical solution at which the surface of the iron, steel or alloy specimens com- 40 bines with the oxygen of the solution. For

this object I preferably employ a watery solution, which contains an oxidizing agent and a certain amountof the reaction products,

which are formed during the reaction between iron and the chemical solution and which hereinafter are termed reaction products the said solution being preferably. in a boiling state.

The signs of oxidation on the specimens of iron, steel or alloys appear in colours of different kind and in different shapes, viz as points or dots, lines or specks, distributed over the specimen to a greater or smaller extent. Sometimes the whole surface. of the specimen is covered therewith. This greatly depends from the homogen'eityof the alloys.

For determining the temperature I preferably use a thermometer and proceed in. such a manner, that I immerse into the heated bath above mentioned all the specimens which are to be examined. Now I further heat the bath referably until it is boiling and remove rom time to time. the specimens from the bath after having noted the temperature of the latter. By examining the specimens after their withdrawal from the bath I note at what temperature the oxidation has taken place. This temperature correspond toa certain critical concentration of the bath, because the same is open, so that water continuously evaporates from the bath. The observations may be made for instance from degree to degree. Usually the signs of oxidation appear suddenly as soon as the corresponding temperature and density in the solution is attained. The colorations of the oxidized specimens arenot in all cases the same but dependessentially on the chemical nature of the additions to the iron or steel.

As the baths which I employ mostly contain a caustic alkali, the same takes up carbonic acid from the air. In order-to remedy this drawback I add caustic lime to the bath occasionally.

The invention may be carried .out according to the following example I prepare a hot solution of 100, parts of caustic soda solution of 33%, 10 parts of sodium nitrate and a small quantit of the reaction products and maintain the a kalinity by adding caustic lime from time to time. The bath thus prepared is heated until it is boiling, and the specimens to be examined are placed simultaneously into the bath, thus under like or the same conditions, for instance bv means of'a dipping device; In order to obtain com arable results it is neces sary, that the sur aces of the said specimens have been treated in like manner, for instance cleaned by means of emery.

7 Now I determine at what temperature and thus also at what concentration of the boiling solution the oxidation. of the individual specimensbegins, this being indicated by a coloration of the specimen.

For instance at the beginning of the process the boiling bath may have a temperature of 130 centigrade. I immerse the specimens into the bath and from time to time I note whether any of the specimens has cxidized. 110

11 loans temperature of the bath and thus also at what concentration of the bath the tested specimens beginto oxidize. I have found,

that the conduct of the iron, steel and the iron or steel alloys in this bath constitutes a for determining their resistance against rusting, so that the specimens which oxidize at the higher temperature in the bath F z'rst example.

Common iron and the rust-proof steels of well-known steel-works, treated in the bath above stated, showed the following figures Iron Steel No.1 StoelNo.II Steel NoJII Steel No. 1v Steel N0.V

show the first sign of oxidation at Second ema/mple.

, A steel alloy with the same contents of carbon and manganese, but containing different amounts of chrome as an alloy-addition gave the following test I Chrome 2% 4% 8% 6% showed the first sign of oxidation at 140 0. 149 o.- 158 0. 190 0. None up to 210 o.

Third example.

If the chrome-steel alloy of 8% is systematically alloyed with nickel, vanadium, cobalt,

titanium' and so forth, I obtain a scale of invention maybe employed also other oxidizing solutions, such as caustic potash solution added with an oxidizing agent. Instead of using sodium nitrate as an oxidizing means I may apply the nitrate of potassium or any other appropriate oxidizing substance.

I claim- 1. Process for ascertaining systematically and quickly the degree of absolute or relative rust-resistance of iron, steel and iron alloys, consisting in determining the aflinity of oxygen to iron, steel and iron alloys by im-. mersing the specimens to be examined into a hot-oxidizing solution and measuring from time to time the temperature of the solution in order to determine the temperature at the moment at which the surface of the immersed specimen combines with the oxygen of the solution.

2. Process for ascertaining systematically and quickly the degree of absolute or relative rust-resistance of iron, steel and iron alloys,

consisting in determining the aflinity of oxygen to iron, steel and lron alloys by immersing the specimens to be examined into a boiling alkaline solution, containing an oxidizing agent and a small amount of the reaction products produced by the action of the said solution on iron, and measuring from time to time the temperature of the solution in order to determine the temperature at the moment at which the surface of the immersed specimen combines with the oxygen of the solution.

3. Process for ascertainin systematically and quickly the degree of a solute or relative rust-resistance of iron, steel and iron alloys, consisting in determining the aflinit'y of oxygen to iron, steel'and iron alloys by immersing the specimens to be examined into a hot solution composed of water, caustic soda, an oxidizing agent and reaction products produced by the action of the said solution on iron and measuring from time to time the temperature of the solution in order to determine the temperature at the moment at which the surface of the immersed specimen combines with the oxygen of the solution.

4. Process for ascertaining systematically and quickly the degree of absolute or relative dust-resistance of iron, steel and iron alloys, consisting in determining the aflinity of oxygen toiron, steel and iron alloys b immersing the specimens to be examined mto a hot solution composed of 100 parts of caustic soda solution of 33% calculated on caustic soda, 10 parts of sodium nitrate and a. small amount of the reaction products produced by the action of the said solution on iron and' measuring from timeto timethe temperature of the solution in order to determine the temperature at the moment at which the surface of the. immersed specimen combines with the oxygen of the solution.

5. Processfor ascertaining systematically and quickly the degree of absolute or relative rust-resistam-e of iron, steel and iron alloys, consisting in determining the affinity of oxygen to iron, Steel and iron alloys by immersing the specimens to be examined into ahoil-' ing alkaline solution containin an oxidizing-agent and a small amount ot the reaction products produced by the action of the said solution on'iron, regenerating from time'to time the alkalinity of the solution I) addin an appropriate amount of caustic ime a-n measuring from time to time the temperature of the solution in order to determine the temperature at the momentat which the surface of'thc immersed specimen combines with the oxygen of the solution.

'6. Process for ascertaining systematically and quickly the degree ofabsolute or relative dust-resistance if iron, steel and iron alloys, consisting in determining the aflinity of oxygen to iron, steel and iron alloys by immersing the specimens to be examined into a boilin alkaline solution, containing an oxidizing agent'and measuring from time to time the temperature of the solution in order to determine the temperature at the moment t at which the surface of the immersed specisignature.

en combines -w'ith the oxygen off'the solu- 

